This invention relates to a photodetector useful in the near infrared portion of the spectrum, for example, at about 1.06 micrometers.
The near infrared wavelengths between about 0.8 .mu. m and about 1.3 .mu. m have recently acquired significance as the wavelengths of interest for future optical fiber communication systems. Such systems have the potential of supplying very large communication bandwidth, when appropriately implemented.
Intensive research has been directed toward the achievement of suitable components for such a system. One of the needed components is a photodetector. This is especially true since the standard silicon diode photodetector is of diminishing efficiency at wavelengths longer than about 1 .mu.m.
A number of exotic photodetectors of semiconducting compounds have been proposed; but many of them have either slow response times or excessive dark currents, partly because of their relatively small semiconductive bandgap energies.
An additional drawback to such new detectors is that many of them use relatively untried material systems. Next to the well-known silicon and germanium semiconductive material systems, the gallium arsenide material system is one of the most extensively investigated and developed material systems.
Therefore, it would be desirable to have a new and efficient photodetector element for the near infrared region of the spectrum which is compatible with the gallium arsenide material system at least to the extent of using gallium arsenide single crystal substrates. Indeed, it is contemplated that several types of gallium arsenide devices may be used in apparatuses designed to be compatible with fused silica optical fiber communication systems.
While some devices using possibly compatible diodes have been proposed, each has a drawback from the viewpoint of overall efficiency. For example, the gallium arsenide antimonide photodetector described by R. C. Eden, Proceedings of the IEEE, Volume 63, Page 32, Jan. 1, 1975, uses the so-called inverted configuration, so that the photons must travel through the relatively thick substrate and therefore suffer excessive free carrier loss.